(Apologies if this is a really obvious question, it's all a bit new for me.)
I'm researching ways I can make the sound coming out of the audio jack of a smartphone comparable between smartphone models. For example, I want to pump out a sound of certain energy ("sound power?") at
x MHz from an app for, say, a Samsung S5 and an iPhone 6. Within software (Android/iOS) I can set a % volume to output, but calculating dB level is challenging because it's a relative value and you don't really know where 0dB is.
It occurred to me that there must be some device (surely?? :-) ) that I can connect to the audio jack that can measure the actual output after impedance of the hardware within the phone. So the set up would be:
iPhone --> [DEVICE] --> Headphones Samsung --> [DEVICE] --> Headphones
Main Question: I don't know if such a device exists, and if it does exist what it would be called?
The idea here is how much measure sound power (a la https://en.wikipedia.org/wiki/Sound_power) is going into the headphones. That leaves interpretation of what 0dB is to the wayside and I can properly compare (and therefore calibrate within software) what % volume I should be using for iPhone and Samsung to output the same energy.
For example I could calculate, on average, that iPhone 6 and Samsung S5 pump out the same sound power at 31% and 33% volume at 1Mhz respectively; I can now use that "calibration" to asses 0 dB through a decent set of headphones via a different investigatory technique (now that I'm sure they're both pumping out the same "volume" level under the same air pressure conditions).